WDM-PON access network technologies have been developed for many years, a technical bottleneck of which is about colorless ONU module. Earlier technology on colorless ONU module based on injection-locked multichannel laser has been proven unsuitable for use in high-rate. In recent years, with the increasing requirements on access bandwidth, WDM-PON access network has been turning to use multi-channel tunable lasers to realize function of colorless ONU.
As known in the art, the multi-channel tunable laser was developed rapidly in recent years. Product of multi-channel tunable laser based on SGDBR (Sampled Grating Distributed Bragg Reflector) was widely applied in 10 Gb/s and 40 Gb/s system. Advanced tunable lasers based on external cavity laser and some special semiconductor even can be applied successfully in 100 Gb/s coherent system. It is technically feasible to use these lasers to achieve colorless ONU function. However, due to complex manufacturing process of the multi-channel tunable laser, and its huge amount of data calibration in multi-channel and wide temperature range, production costs thereof are always high. High cost of ONU devices has been bottleneck for large-scale application of WDM-PON technology.
How to reduce the cost of a colorless ONU as far as possible with meeting application requirements of WDM-PON access network is a key issue in current field. The multi-channel tunable laser is key factor to address the issue, since the multi-channel tunable lasers accounted for most of the hardware cost of the ONU. In recent years, it is also proposed some targeted tunable laser solutions for WDM-PON, such as a solution based on gain dies plus external cavity tunable grating structure, as well as a solution based on gain dies plus external cavity double resonant loop tuning, and even a solution directly using a semiconductor integrated tunable laser die similar with SGBDR, and so on. These production techniques shared similar ideas on dealing with wavelength channel power-on accuracy and wavelength stability control in operation, namely, which are realized by self-monitoring and control of laser, which will increase technical complexity of the multi-channel tunable lasers, including high standards of hardware requirements, and complex and time-consuming workload of calibration and testing.